Thermopiles are customarily implemented in commercial applications and utilized for thermal detectors such as infrared (IR) detecting sensors. IR sensors that include thermopiles, comprised of sets of thermocouples, are used in a wide range of applications, such as automotive climate control systems and seat occupancy detection systems. An integrated thermopile-based IR sensor that combines circuitry for processing and compensating output signals of the sensor on an integrated circuit (IC) chip is described in U.S. Pat. No. 6,828,172, titled “Process for a Monolithically-Integrated Micromachined Sensor and Circuit,” to Chavan et al. and U.S. Pat. No. 6,793,389, titled “Monolithically-Integrated Infrared Sensor,” to Chavan et al., each of which are hereby incorporated herein by reference in their entirety. As described, integration of IR sensing and signal processing on the same IC chip leads to various advantages, which include miniaturization, the ability to process very small signals, reduction in cost, simplification of manufacturing and reduced system complexity. Further performance and manufacturing optimization through the creation of a circular membrane and thermopile is described in U.S. patent application Ser. No. 11/263,105, titled, “Infrared Detecting Device with a Circular Membrane.”
IR detecting sensors frequently use thermopiles having sets of thermocouples. One end of each set of the thermocouple is situated on a membrane or diaphragm that collects IR energy (a thermally isolated region), and a different end is situated on a supporting substrate (a thermally sunk region). The formation of a thermopile uses a series of electrically connected thermocouples, each made up of dissimilar conducting or semi-conducting materials with different Seebeck coefficients, whereby thermal energy is converted into an electric voltage. This is conventionally achieved through the use of a pair of materials such as two dissimilar metals, including n-type poly-silicon and metal, p-type poly-silicon and metal, or n-type poly-silicon and p-type poly-silicon. The connections are made such that they alternate between the thermally isolated and thermally sunk regions of the device. The dissimilar materials are typically arranged either in a horizontal or vertical stack and separated (i.e., electrically isolated) by a dielectric material. This is customarily achieved by separate material depositions, photolithographic operations, and etching for each material.
FIG. 1 and FIG. 2 are plan views of a conventional vertical thermocouple arrangement. In FIG. 1, the IR detecting device 100 utilizes a first material 104 and a second material 106, which are dissimilar materials. These may be, for example, p-type poly-silicon and metal. The second material 106 is formed on top of, and electrically isolated from, the first material 104. In FIG. 2, the IR detecting device 200 utilizes a first material 204 and a second material 206, which are dissimilar materials. These may be, for example, n-type poly-silicon and metal. The second material 206 is formed along the side of the first material 204, separated by a dielectric material. With respect to the formation of the conventional IR detecting devices 100 and 200, both the physical separation by the dielectric material and the separate process steps required for the formation of each leg of the thermocouple create a considerable non-active area which consumes valuable diaphragm area, and thus reduces output signal per unit diaphragm area.